Field production of cannas in the United States is difficult to estimate (Johnson et al., 1995), although in Texas it may be about 750 acres, primarily for rhizome seed stock production. Weed control in cannas and other ornamental crops is difficult due to an insufficient number of registered herbicides that provide soil residual (Collins et al., 2001). Herbicide use can be expensive compared with standard row crop production, and many herbicide registrations are limited to containerized crops and landscape use. Crop rotation can be a useful tool for integrated weed management, especially against perennial weeds like nutsedge (Warren and Coble, 1999). However, canna production is most successful on sandy soils, which are ideal for nutsedge growth, and rotation may be limited. Increased irrigation, required for good canna production, also reduces herbicide efficacy through leaching.
Weeds found in production fields reduce crop yields by competing for nutrients, moisture, physical space, and light (Bond and Oliver, 2006), and they may also harbor crop insects and diseases. As a result, crop growth is often reduced, and, at harvest, weeds can interfere with equipment and reduce grower profits by increasing crop injury and hand labor (Nowacki, 1983). Between-row weeds can be controlled through herbicides plus cultivation; however, in-row weeds are more difficult to control. Work crews are often employed to remove weeds manually at considerable cost.
Palmer amaranth is a troublesome and competitive broadleaf weed found in many commercial agronomic, vegetable, and ornamental field crops and is common throughout the midsouth and southern high plains of the U.S. (Bond and Oliver, 2006; Morgan et al., 2001). Palmer amaranth plants may grow over 1.0 m above crop canopies, shading crops and reducing their photosynthetic and reproductive capacities. Palmer amaranth may develop extremely thick stems and root systems weighing up to 5 kg each, causing significant problems during crop harvests (Keeley et al., 1987). Increasing resistance to dinitroaniline herbicides as well as the recent discovery of glyphosate resistance creates the need to find additional herbicides for use in weed management programs (Gossett et al., 1992; Scott and Smith, 2006).
Yellow nutsedge (Cyperus esculentus) and purple nutsedge (C. rotundus) continue to be serious problems in agronomic and nursery crops throughout the southern U.S., not only through weed competition but also through the infestation of tubers in products sold (Beste and Frank, 1990; Collins et al., 2001; Webster and Coble, 1997). Nutsedge tubers may be disseminated to homeowners through retailers or to other grower fields. When found in the fields, canna growers regularly hand-pick nutsedge tubers before selling the crop, significantly reducing their profits. Currently, halosulfuron offers fair to good control of nutsedge with post-emergence applications (McDaniel et al., 1999) and has potential for use in large-scale commercial production.
Two herbicides currently registered for nursery production are s-metolachlor and pendimethalin. However, commercial growers are in need of additional herbicides that control adapting weed species or that have longer soil residual (Collins et al., 2001; Gossett et al., 1992). Although s-metolachlor and pendimethalin provide fair to good control of perennial and annual weeds (Richardson and Zandstra, 2006), cultivation and hand-weeding are still required, and this combination offers only fair control of nutsedge. Past research has concentrated on weed control for containerized or landscape ornamentals, but little research has been conducted for large-scale commercial field-grown production. Therefore, research was initiated to determine crop safety and weed control potential of selected herbicides for control of palmer amaranth and nutsedge under field-grown conditions for canna rhizome production.
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